1. Field of the Invention
The invention concerns a palette changer for machine tools wherein a palette is pushed by means of a swing arm from the palette receiver of a sled, over a bridge table, and onto a transfer station. The palette changer can achieve a change of palettes with minimal idle time and utilizes a palette receiver which is slidable in a single direction.
2. Description of the Related Art
A palette changer of this category is known from EP 0 281 664 B1. With this type of known palette changer, a palette receiver slidable in the X-direction is provided upon a sled which is slidable in the Y-direction. On the palette receiver, a swing arm is mounted pivotable about an axis perpendicular to the X-Y-plane. A pinion mounted on the axis of the swing arm engages with a rack mounted on the sled in order to swing the swing arm, when the palette receiver is slid upon the sled in the X-direction. The swing arm engages with a roller provided on its free end in a groove in the palette, in order to slide the palette during the swinging movement of the swing arm. For a palette exchange the palette receiver is hydraulically raised, in order axially to slide the pinion of the swing arm and to bring it into engagement with the rack. Thereafter, the palette receiver is slid in the X-direction whereby the palette is slid from the palette receiver with high speed in the X-direction in correspondence to the radius relationship of the swing arm and pinion. As soon as the palette with its work pieces to be processed is slid from the palette receiver to a holding position A, the sled is pushed in the Y-direction in order that the swing arm with its roller is brought into engagement with a palette with unprocessed work pieces which are to be found in a holding position B. Thereafter, the palette receiver is again pushed back in the X-direction whereby the swing arm is pivoted back and shoves the palette with its unprocessed work pieces onto the palette receiver. By lowering of the palette receiver the palette is tensioned and indexed.
The lifting off of the palette receiver for the palette exchange and for the engagement of the pinion of the swing arm complicates the construction. The palette changer pushes the palette from the palette receiver to an immediately adjacent first waiting position and takes over the palette from a likewise immediately adjacent second waiting position, whereby the two waiting positions are positioned in a common plane next to each other. The spatial separation of the waiting positions from the working room of the two machines is inadequate. Besides this the necessity of two waiting positions situated on the same plane adjacent to each other compromises the flexibility of the construction of the work tools and in the utilization possibilities of a palette storage. Finally, the palette changer requires movement of the palette receiver in two axis, namely in X-direction and the Y-direction, so that the palette changer is not suitable for work machines, such as for example processing centers, in which the palette reception is only slidable in a single spatial axis, because the movement in the other two spatial axes is taken up by the travel path of the work tools.